A standard coal-dust gasifying apparatus such as described in German patent document No. 2,705,558 has a housing with an output fitting for the removal of generator gas and an output fitting for the removal of granulated slag, a funnel guide for conducting granulated slag in the housing to the slag-output fitting, a coal-dust burner capable of forming a coal-dust flame in an upper reaction zone of the housing, and an overflow apparatus for maintaining a body of liquid in the bottom of the housing. A high-temperature thermal protection lining is provided in the upper reaction zone of the housing and this reaction zone has a restricted lower end. A laterally gastight tube wall in the housing in a lower cooling zone beneath the reaction zone has upper and lower manifolds and radially inwardly delimits an axially extending annular passage radially outwardly defined by the housing.
Such an arrangement has substantial disadvantages. First of all the thermal lining of the reaction zone is rapidly eroded by the molten particles of slag present in this region. In fact a standard refractory lining is eroded from 10 mm to 40 mm in 200 h of operation, whereupon the apparatus must be shut down and relined. In addition the molten slag solidifies in the restricted lower end of the thermal lining and crusts on the lining at this level. This further restricts flow through the apparatus by clogging it at this critical level and considerably reduces operating efficiency. In addition the still molten paticles in the downwardly moving gas stream stick to the cool walls of the tube wall and crust up thereon also. The result of this is another restriction of flow and a substantial loss of heat-exchange efficiency so that the apparatus is less efficient with reduced throughput and a hotter output gas, and needs frequent opening and cleaning.
In Russian patent document No. 3,359,368 an arrangement is described of the above-described type wherein the tube wall is restricted centrally to form an upper reaction zone and a lower radiation or cooling zone. The gas outlet opens into the cooling zone and the tube wall is studded in the reaction zone so it can carry a layer of insulating material. The lower part of the tube wall is formed of two concentrically arranged and radially gastight portions, forming upper and lower radial throughgoing openings by bending in and out the individual tubes.
In such an apparatus the gas temperature upstream of the central restriction of the tube wall is 100.degree. C. to 200.degree. C. above the melting temperature of the slag, so that more heat must be dissipated downstream in the cooling zone. The overall operation temperature of the apparatus is therefore increased considerably so that some of the product gas is combusted, thereby substantially reducing the efficiency of the system both by wasting the product and raising the product's temperature. In addition the lining of the upper portion of the tube wall is subjected to very high temperatures and therefore has a very short service life. What is more the slag can crust up at the upstream end of the cooling zone as in the other above-described system. Finally, the use of a centrally restricted apparatus necessitates operating the system at substantially higher input pressure, which once again represents a reduction in operating efficiency.